The present invention relates to a capacitor of an MIM (Metal-Insulator-Metal) structure, more specifically a capacitor which can prevent peeling at the interface between the electrode and the capacitor dielectric film and deterioration of capacitor characteristics due to thermal processing and a method for fabricating the capacitor, and a method for fabricating a semiconductor device including such the capacitor.
DRAM is a semiconductor memory device which can be constituted by one transistor and one capacitor, and have been studied in structures and methods for fabricating semiconductor memory devices of high density and high integration. Especially areas occupied by capacitors much influence integration of devices, so that it is very important how to increase a capacitance per a unit area. To this end, for DRAM of giga-bit storage capacities, which have been recently developed, it has been studied in order to decrease areas occupied by the capacitors that the capacitor dielectric film is formed of metal oxide, whose dielectric constant is higher than those of silicon oxide film and silicon nitride film, which have been conventionally widely used. As such oxide dielectric films, oxide dielectric film, such as tantalum oxide film, BSTO film, STO film, PZT film, etc., have been studied.
Such oxide dielectric films as the capacitor dielectric film have been usually formed by CVD method. This is because the films formed by CVD method have high dielectric constants, low leakage current, and good step coverage. As electrode materials, noble metal material as of ruthenium (Ru) have been used. This is because noble metal films have good adhesion to oxide dielectric films and can form capacitors having large work function difference and low leakage current.
However, the inventors of the present application made various studies and have found that when an upper electrode is formed of a metal material on the oxide dielectric film, peeling at the interface between the oxide dielectric film and the upper electrode takes place due to later thermal processing.
In the usual semiconductor process, thermal processing after the uppermost passivation film has been formed is performed in a forming gas atmosphere for improving transistor characteristics. However, this thermal processing has often degraded electric characteristics of the capacitor.
An object of the present invention is to provide a semiconductor device and a method for fabricating the same which can prevent peeling between the upper electrode and the oxide dielectric film and can suppress capacitor characteristic degradation.
According to one aspect of the present invention, there is provided a capacitor comprising: a lower electrode of a metal; a capacitor dielectric film of an oxide dielectric film formed on the lower electrode; and an upper electrode of a metal formed on the capacitor dielectric film, an impurity concentration in the lower electrode being different from that in the upper electrode.
According to another aspect of the present invention, there is provided a method for fabricating a capacitor comprising the steps of: forming a lower electrode of a metal over a substrate; forming a capacitor dielectric film of an oxide dielectric film on the lower electrode; depositing a metal film on the capacitor dielectric film; performing a thermal processing in a hydrogen-content atmosphere after the step of depositing the metal film; and patterning the metal film to form an upper electrode of the metal film after the step of performing the thermal processing.
According to further another aspect of the present invention, there is provided a method for fabricating a capacitor comprising the steps of: forming a lower electrode of a metal over a substrate; forming a capacitor dielectric film of an oxide dielectric film on the lower electrode; and forming an upper electrode of a metal on the capacitor dielectric film, conditions for forming the lower electrode and the upper electrode being controlled so that an oxygen concentration in the upper electrode is higher than that in the lower electrode.
According to further another aspect of the present invention, there is provided a method for fabricating a semiconductor device comprising the steps of: forming a lower electrode of a metal over a semiconductor substrate; forming a capacitor dielectric film of an oxide dielectric film on the lower electrode; depositing a metal film on the capacitor dielectric film; performing a thermal processing in a hydrogen-content atmosphere after the step of depositing the metal film; and patterning the metal film to form an upper electrode of the metal film after the step of performing the thermal processing.
According to further another aspect of the present invention, there is provided a method for fabricating a semiconductor device comprising the steps of: forming a lower electrode of a metal over a semiconductor substrate; forming a capacitor dielectric film of an oxide dielectric film on the lower electrode; forming an upper electrode of a metal on the capacitor dielectric film; performing a thermal processing in a hydrogen-content atmosphere after the step of forming the upper electrode; and forming an uppermost passivation film over the upper electrode after the step of performing the thermal processing.
As described above, according to the present invention, thermal processing is performed in a hydrogen-content atmosphere after a metal film to be the upper electrode has been deposited and before the patterning, whereby a carbon concentration of the upper electrode is decreased to thereby improve the adhesion between the capacitor dielectric film and the upper electrode, which prevents the peeling of the upper electrode.
The metal film to be the upper electrode is formed under conditions which allow the upper electrode contain a high concentration of oxygen, whereby the adhesion between the capacitor dielectric film and the upper electrode can be improved, which prevents the peeling of the upper electrode.
Thermal processing is performed in a hydrogen-content atmosphere after the upper electrode has been formed and before the uppermost passivation film is formed, whereby damage in the back end process can be decreased, which can improve capacitor characteristics.